1. Field of the Invention
The present invention relates to a variable time lag camera in which the release time lag (i.e., the time between the output of a release signal and the time that the camera shutter begins moving) can be set.
2. Description of Related Art
In single-lens reflex cameras, the camera can shake due to vibrations caused by such things as the movement of the mirror when the mirror is moved upward and by the jolt associated with the mirror movement. Accordingly, in conventional single-lens reflex cameras, a release time lag exists between the output of the release signal (generated, for example, when the camera user presses a release button downward) and the start of movement of the front shutter curtain. This release time is provided to allow for the mirror movement or for autofocusing of the lens prior to film exposure. Because of this release time lag, the front shutter curtain does not start moving until several tens of milliseconds have elapsed after generation of the release signal.
When a camera is operated in continuous photography mode, in which several frames (i.e., photographs) are taken continuously (i.e., several photographs are taken sequentially for a single actuation of the release button), it is desirable to have a short release time lag for each frame. This will enable the time between each photograph to be short, and will make full use of the high speed frame (film) advance capabilities of the camera.
However, in single-lens reflex cameras, the camera can shake due to vibrations caused by such things as movement of the mirror as detailed above. Consequently, problems such as multiple exposures or blurring may result if some minimum time lag is not used for each frame.
Thus, from the standpoint of camera movement, a long release time lag is desirable because it allows time for stabilizing the camera movement. Because, as explained above, a short release time lag is desired for the continuous photography mode, the length of the release time lag must be reset (i.e., shortened) or the speed of the frame advance will drop.
U.S. Pat. No. 4,969,003 discloses a single-reflex camera including an autofocus device. Time lag associated with typical single-reflex cameras is discussed on column 1, lines 32-47 and column 7, lines 30-53. A release subroutine that is used for single frame mode is detailed on column 17, line 52--column 18, line 35, and differs from a release subroutine used for continuous photography mode, as detailed on column 18, line 60--column 19, line 46. In particular, the values of variables used in an autofocus procedure are not reset between frames when the camera operates in the continuous photography mode so that the frame rate (i.e., the rate at which photographs are taken) can be maintained at a high level.